docs: def has_tag(self, p_key, p_value=""):
          """
          Returns true when there is at least one tag with the given key. If a
          value is passed, it will only return true when there exists a tag with
          the given key-value combination.
          """
          tags = self.fields['tags']
          return p_key in tags and (p_value == "" or p_value in tags[p_key])